tracetool/syslog: add Rust support

The syslog backend needs the syslog function from libc and the LOG_INFO enum
value; they are re-exported as "::trace::syslog" and "::trace::LOG_INFO"
so that device crates do not all have to add the libc dependency, but
otherwise there is nothing special.

Signed-off-by: Tanish Desai <tanishdesai37@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20250929154938.594389-17-pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

rust/Cargo.lock

@@ -262,6 +262,9 @@ dependencies = [
 [[package]]
 name = "trace"
 version = "0.1.0"
+dependencies = [
+ "libc",
+]
 
 [[package]]
 name = "unicode-ident"

rust/trace/Cargo.toml

@@ -12,5 +12,8 @@ license.workspace = true
 repository.workspace = true
 rust-version.workspace = true
 
+[dependencies]
+libc = { workspace = true }
+
 [lints]
 workspace = true

rust/trace/src/lib.rs

@@ -3,6 +3,10 @@
 //! This crate provides macros that aid in using QEMU's tracepoint
 //! functionality.
 
+#[doc(hidden)]
+/// Re-exported item to avoid adding libc as a dependency everywhere.
+pub use libc::{syslog, LOG_INFO};
+
 #[macro_export]
 /// Define the trace-points from the named directory (which should have slashes
 /// replaced by underscore characters) as functions in a module called `trace`.

scripts/tracetool/backend/syslog.py

@@ -12,7 +12,7 @@ __maintainer__ = "Stefan Hajnoczi"
 __email__      = "stefanha@redhat.com"
 
 
-from tracetool import out
+from tracetool import out, expand_format_string
 
 
 PUBLIC = True
@@ -38,6 +38,11 @@ def generate_h(event, group):
         fmt=event.fmt.rstrip("\n"),
         argnames=argnames)
 
+def generate_rs(event, group):
+    out('        let format_string = c"%(fmt)s";',
+        '        unsafe {::trace::syslog(::trace::LOG_INFO, format_string.as_ptr() as *const c_char, %(args)s);}',
+        fmt=expand_format_string(event.fmt),
+        args=event.args.rust_call_varargs())
 
 def generate_h_backend_dstate(event, group):
     out('    trace_event_get_state_dynamic_by_id(%(event_id)s) || \\',

tests/tracetool/syslog.rs

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+// This file is @generated by tracetool, do not edit.
+
+#[allow(unused_imports)]
+use std::ffi::c_char;
+#[allow(unused_imports)]
+use util::bindings;
+
+#[inline(always)]
+fn trace_event_state_is_enabled(dstate: u16) -> bool {
+    (unsafe { trace_events_enabled_count }) != 0 && dstate != 0
+}
+
+extern "C" {
+    static mut trace_events_enabled_count: u32;
+}
+extern "C" {
+    static mut _TRACE_TEST_BLAH_DSTATE: u16;
+    static mut _TRACE_TEST_WIBBLE_DSTATE: u16;
+}
+
+#[inline(always)]
+#[allow(dead_code)]
+pub fn trace_test_blah(_context: *mut (), _filename: &std::ffi::CStr)
+{
+    if trace_event_state_is_enabled(unsafe { _TRACE_TEST_BLAH_DSTATE}) {
+        let format_string = c"Blah context=%p filename=%s";
+        unsafe {::trace::syslog(::trace::LOG_INFO, format_string.as_ptr() as *const c_char, _context /* as *mut () */, _filename.as_ptr());}
+    }
+}
+
+#[inline(always)]
+#[allow(dead_code)]
+pub fn trace_test_wibble(_context: *mut (), _value: std::ffi::c_int)
+{
+    if trace_event_state_is_enabled(unsafe { _TRACE_TEST_WIBBLE_DSTATE}) {
+        let format_string = c"Wibble context=%p value=%d";
+        unsafe {::trace::syslog(::trace::LOG_INFO, format_string.as_ptr() as *const c_char, _context /* as *mut () */, _value /* as std::ffi::c_int */);}
+    }
+}

tests/tracetool/tracetool-test.py

@@ -14,7 +14,7 @@ def get_formats(backend):
         "c",
         "h",
     ]
-    if backend in {"ftrace", "log", "simple"}:
+    if backend in {"ftrace", "log", "simple", "syslog"}:
         formats += ["rs"]
     if backend == "dtrace":
         formats += [